1. Field of the Invention
This invention relates to a speed reducer which has a simple in structure but can provide a large reduction ratio.
2. Description of the Related Art
Conventional speed reducers include ones comprising a plurality of spur gears combined in the form of a gear train, one comprising planet gears and ones using pulleys and belts.
Any of such conventional speed reducers can provide only a small reduction ratio. In order to increase the reduction ratio, it was necessary to use a large number of gears or to use worm gears. Either of these solutions leads to an increase in the size of the device or to a reduction in the power transmission efficiency.